In many systems, proper operation requires information regarding the position of a rotating, or partially rotating, component such as on a steering column or a throttle. Known propulsion systems use redundant motors and drives where it is necessary to determine the position of a rotor shaft to ensure proper operation.
As shown in FIG. 1, a motor 100 includes a rotor shaft 102 with a magnetic wheel 104 attached to the rotor shaft 102. A printed circuit board (PCB) 106 includes a number of Hall effect sensors 108, for example six (6) sensors, to determine a position of the rotor shaft 102 by detecting the orientation of the magnetic field of the spinning magnetic wheel 104. As known, the rotational position of the rotor shaft 102 is used to control the current that is commanded to the various phase windings of the motor. It is critical that an accurate position of the rotor 102 be known in order to provide currents to the motor windings that are in phase with the magnetic fields.
An “on-axis” magnetic encoder or sensor 200 is known in the field of position sensing, as shown in FIG. 2. The sensor detects a magnetic field and one such sensor is the AS5047P “14-Bit On-Axis Magnetic Rotary Position Sensor” from austriamicrosystems AG of Unterpremstaetten, Austria. With an on-axis encoder 200, a magnet 202 is attached to the spinning part, e.g., a motor shaft, and the sensor 200 is positioned adjacent the magnet 202 such that a magnetic field 204 from the magnet 202 is sensed in the encoder 200. In most cases, it is necessary that the magnet 202 be directly over the top, i.e., a field sensing surface, of the sensor 200 and within relatively narrow positional location and axial alignment constraints.
Some of the known “on-axis” encoders have a plurality of sensors embedded either in one integrated circuit (IC) or provided in a single package. These “multi-sensor” ICs are used in safety critical systems such as steering, throttle and brake applications. Recently, there has been a push to design safety systems that are capable, on their own, of detecting a fault and determining the best means to correct the fault. As a result, any sensor system that is used must have the ability to verify its own data. In the case of a position sensor, however, two galvanically isolated systems are needed for the system to verify the data of any individual sensor.
Several manufactures have begun to build “redundant sensors” with two galvanically isolated chips manufactured into one IC package. Such an example is the AMS S5215 “Programmable 360° Magnetic Angle Encoder with Buffered SINE & COSINE Output Signals” available from austriamicrosystems AG. The AMS S5215 includes two independent dies in one package to provide redundancy where a bottom die, which is exposed to a slightly less magnetic field, is used for a “plausibility check.”
While having multiple dies in one package provides some amount of redundancy, the layout of the pins on the package prohibits a truly redundant solution. As shown in FIG. 3, the pins of the AMS S5215 integrated circuit device, for example, are arranged such that a simple short-circuit between two adjacent pins, such as pins 27 and 28 for receiving the digital and analog power, respectively, or a high voltage pulse to a set of adjacent pins, could short circuit and destroy both sensors in the package.
What is needed is a system for providing redundant and reliable position sensing of a rotating component.